Cambridge , Massachusetts -LRB- CNN -RRB- -- Millions of Iranians poured into the streets Saturday to celebrate the victory of presidential candidate Hassan Rouhani . Huge crowds snarled traffic in the capital , Tehran , demanding the release of hundreds of political prisoners arrested during protests over sham elections four years ago . `` My dead brother and sister , I got your vote back , '' people chanted , a reference to more than 100 demonstrators killed by the regime .

The surprise was not so much that 18 million votes were cast for Rouhani , slightly more than half the ballots , but the fact that the regime had endorsed his victory , triggering hope that international pressure over Iran 's nuclear program and growing internal rifts at home might have forced the leadership to restore some of its lost legitimacy .

Rouhani is not a reformist , even according to Iranian standards . He had backed the violent crackdown against the pro-democracy student movement in 1999 and never formally aligned himself with the reformist camp . A cleric and a veteran politician since 1979 , he was in the circle close to the founder of the revolution , Ayatollah Khomeini . He served five terms as a member of Parliament and 16 years as the head of the National Security Council .

During the campaign , he presented himself as a moderate , a platform that appeals to Iran 's young electorate , and called for drawing Iran out of its international isolation . `` It is important for the centrifuges to spin , but people 's lives should run too , '' he said in a televised address , referring to uranium enrichment . He gained momentum only a few days before the election when two former presidents , both aligned with the reformers , Mohammad Khatami and Akbar Hashemi Rafsanjani , threw their support behind him . Then voters decided to give the polls , as a window to exercise their democratic rights , another try .

Ironically , Rouhani , the only cleric among the eight candidates , favors more political and social freedoms at home . During one of his talks , his supporters chanted slogans demanding the release of opposition leaders , Mehdi Karroubi and Mir Hossein Moussavi , the two presidential candidates in 2009 who have been under house arrest for two years .

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The Supreme Leader Ayatollah Ali Khamenei , along with his military loyalists , the Revolutionary Guards and its militia wing Basij -- the alliance that many believe stole the election in favor of the incumbent Mahmoud Ahmadinejad -- still remain in ultimate power . Many had suspected that the regime would go to extraordinary lengths , as it did in 2009 , to manage the vote from start to finish .

The Guards and the Basij campaigned vigorously for Saeed Jalili , a Khamenei loyalist and Iran 's hard-line nuclear negotiator . His loss with less than 15 % of the vote was an embarrassing rebuke of Khamenei 's policies . Last month , demonstrators chanted `` Death to Dictator , '' meaning Khamenei , at the funeral of a dissident cleric in the city of Isfahan . So by giving in to Rouhani 's victory , many believe Khamenei is trying fix his tattered image .

Rouhani is Iran 's next president

Although the election was far from democratic , it provided an opportunity for many Iranians , especially the young , to break the deadly atmosphere of fear the government has imposed for the past four years . The watchdog Guardian Council had already helped Khamenei sideline his rivals , barring a prominent politician and a former president , Rafsanjani , from running in the race . Government forces arrested activists and campaigners in the months before the election .

Economic issues were paramount on the minds of voters as U.S.-led sanctions have reduced Iran 's oil revenue by half and shot the inflation rate up to more than 30 % . Voters recalled Rouhani as the county 's pragmatist nuclear envoy who deterred threats in 2003 by signing the Additional Protocol , allowing inspectors from the International Atomic Energy Agency to visit Iran 's nuclear facilities .

Further , Iran suspended its sensitive uranium enrichment activities , a process that can be used to make nuclear fuel or a nuclear bomb if uranium is enriched to high levels . Those measures built trust around Iran 's nuclear program until Ahmadinejad reversed them in 2005 .

It is not clear if Khamenei 's hard-line allies will allow Rouhani to introduce real change . The president sets the tone for domestic and foreign policy and can make room for more moderate voices in politics . But he holds little power compared with the authority that the constitution gives Khamenei . If Khamenei is willing to end international pressure over Iran 's nuclear program , Rouhani provides the perfect opportunity .

Rouhani 's victory has already bolstered a sense of optimism . Iranian currency , the rial , strengthened slightly against the U.S. dollar for the first time on Saturday after its steady downward spiral since 2011 . In his first message after his election , Rouhani declared that `` a new chapter '' has begun and hoped the international community would use a more respectful rhetoric toward Iran .

The opinions expressed in this commentary are solely those of Nazila Fathi .

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Nazila Fathi : Half the votes were for Rouhani , but government 's support is surprising

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Fathi : He supports enrichment of uranium : `` It is important for the centrifuges to spin ''

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Rouhani was the only cleric to run , she says , but he favors political and social freedoms

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Fathi : Victory sparked optimism , hopes for respect from international community